Transformer



Oct. 30, 1934. F 5 LL 1,979,096

TRANSFORMER Filed June 1, 1934 g I j l Z/ l 1 1 1 1 l w I U I 1 I 1 1 I I I 1 I I I J I I Ihventor:

Fred B. S. C-ahall,

His Attorney.

Patented Oct. 30, 1934 UNITED STATE PATENT @FZFEQE TRANSFORMER New York Application June 1, 1934, Serial No. 728,478

4 Claims.

My invention relates to transformers. It is often desirable to connect a voltage responsive instrument, such as a voltmeter, to a transformer winding but the voltage of a transformer wind- 5 ing is often so high that it is not practicable to connect the winding directly to the instrument. The voltage applied to the instrument may be reduced by connecting a step-down transformer between the winding and the instrument but this is expensive and contributes to inaccuracy in the voltage indication of the instrument. The instrument, properly calibrated or adjusted, may be connected to an auxiliary low voltage winding if the auxiliary winding is so arranged that the ratio of its voltage to that of the high voltage winding is constant under all conditions of the transformer load and power factor. This could be done if the high voltage and auxiliary windings could occupy the same position on the transformer core but this is of course impossible. It

has been done or at least approximated by locating the small low voltage auxiliary winding in a space between two sections of the high voltage winding so that the mean radii of the turns in both windings are equal. This, however, makes insulation of the auxiliary winding diificult and the auxiliary winding with its insulation takes up valuable space needed for the high voltage winding. The general object of the invention is to provide a transformer having a high voltage winding with an improved arrangement includ ing an auxiliary winding for producing a voltage substantially proportional to that of the high voltage winding under varying conditions of load and power factor.

The invention will be more fully explained in the following description taken in connection with the accompanying drawing in which Fig. 1 shows a transformer, partly in section, provided 49: with an auxiliary winding arranged in accordance with the invention, and Fig. 2 is a sectional view on the line 22 of Fig. 1.

Like reference characters indicate similar parts in both figures of the drawing.

The transformer shown in the drawing includes a three-legged magnetic core 10 having a center winding leg 11 surrounded by a low voltage winding 12 and a high voltage winding 13. An auxiliary winding including an inner section 14 and an 591 outer section 15 also surrounds the winding leg 11 of the core. The main windings l2 and 13 are of cylindrical form and are concentrically arranged with the low voltage winding 12 next to the winding leg 11 of the core and the high voltage winding 13 spaced around the low voltage winding. The inner section 14 of the auxiliary wind ng is supported in the space 16 between the main. windings l2 and 13 and the outer section 15 of the auxiliary winding is supported outside of and surrounding the high voltage winding 13. The high voltage winding 13 is thus located between the two sections 14 and 15 of the auxiliary winding. The two sections 14 and 15 of the auxiliary winding are connected in series by a conductor 17 extending under the lower edge of the high voltage winding 11. A voltage responsive instrument such as a voltmeter 18 is connected to the auxiliary winding which may be small and of few turns so that its voltage may be low and suitable to apply to the instrument.

If all of the magnetic flux were confined to the body of the core 10 under all conditions of transformer load, then all the turns of the windings would have the same voltage and there would be a constant ratio between the voltages of the high voltage winding 13 and the auxiliary winding. Under load conditions, however, there is a leakage fiux field in the space occupied by the windings and the amount of this leakage flux increases and decreases with the transformer load. The leakage flux field is not uniform at any instant but is strongest near the winding leg 11 and decreases in strength away from this winding leg. Consequently, the eifect of the leakage flux is to cause the voltage of each turn of the winding section is to be a little higher than that of each turn of the high voltage winding 13 and to cause the voltage of each turn of the auxiliary winding section 15 to be a little smaller than that of each turn of the high voltage winding 13. If the total number of turns in the auxiliary winding is properly distributed between the two sections 14 and 15 of the winding, then the excess voltage in the section 14 will exactly balance the deficiency in voltage in the section 15 and the ratio between the total voltage of the auxiliary winding and that of the high voltage winding 13 will be constant under all load conditions.

In order that there may be a proper ratio between the number of turns in the section 14 and that in the section 15 of the auxiliary winding, it is usually necessary that one of the turns be partly in each of these winding sections. For example, suppose the total number of turns in the auxiliary winding is to be 24, then it may happen that 4 turns are necessary in th inside winding section 14 and 19 turns in the outside winding section 15. As indicated in Fig. 2, each section 14 and 15 of the auxiliary winding contains the proper whole number of turns and then a fractional part of a turn, the two partial turns being connected by the conductor 17 extending around the lower edge of the high voltage winding. It will be appreciated from Fig. 2 that that portion of the leakage flux which is between the two sections 14 and 15 of the auxiliary winding surrounds that portion of the divided turn which is in the Winding section 14 but does not surround the other portion of the divided turn which is in the winding section 15. The ratio between the voltage of the high voltage winding and the sum of the voltages of the two winding sections 14 and 15 of the auxiliary winding will therefore remain constant under all load conditions. The instrument 18 may, therefore, be calibrated or adjusted to respond in exact accordance with voltage changes in the high voltage winding 13.

The invention has been explained by describing and illustrating a particular arrangement and application thereof, but it will be obvious that changes may be made without departing from the spirit of the invention and the scope of the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States, is:-

1. A transformer including a main winding, and a sectional auxiliary winding, said main Winding being located between thesections of the auxiliary winding, and said auxiliary winding including one turn located partly in one and partly in the other of its sections.

2. A transformer including a main winding, and a sectional auxiliary winding, said main winding being located between the sections of the auxiliary winding, and one turn of said auxiliary winding being located in parts of the leakage fiux field of different strengths.

3. A transformer including a main winding, and a sectional auxiliary winding with a section inside and another section outside the main winding, one turn of the auxiliary winding being located partly in its inner section and partly in its outer section, and the parts of said turn being connected by a conductor extending around one edge of the main winding.

4. A transformer including a main winding located in a portion of the leakage flux field of the transformer, and an auxiliary winding including two series connected sections, one section of the auxiliary winding being located in a portion of the leakage flux field of greater strength than that occupied by the main winding and one of the turns of the auxiliary winding having a portion in each auxiliary winding section.

FRED B. s. CAHALL. 

